Combustion within gas turbine engines is typically initiated by an ignition system having a heating source. Historically, two different types of igniters have been used, one located within the combustion chamber and the other located outside of the combustion chamber. It is preferred from a durability point of view to have the ignition system located outside of the combustion chamber such that it is not directly in contact with the hot combustion gases that can reduce component life. However, this arrangement requires the ignition system to be extremely reliable given its proximity to the combustible mixture. Because of this reliability issue, a compromise of configurations evolved resulting in a retractable igniter. Once ignition occurs, the igniter is retracted to a position that is a sufficient distance from the hot combustion gases. This system, while effective, requires additional hardware in order to ensure that the igniter is properly positioned at all times.
In an attempt to provide an igniter positioned a sufficient distance from the combustion chamber, torch igniters have often been utilized. A torch igniter is most commonly described as a system that co-locates an ignition source with a fuel injector, which is auxiliary to a combustion system main injector. This igniter geometry is most common in combustion systems operating on liquid fuel, similar to that disclosed in U.S. Pat. No. 5,085,040. One disadvantage to a torch igniter with liquid fuel is the blockage of the fuel injector that can be due to debris or coking of the fuel due to its operating temperature. Should the fuel flow to the torch igniter remain steady in order to limit the amount of coking, even once the combustion chamber is lit, ineffective mixing of the igniter fuel source within the combustion chamber fuel source can produce unnecessary distress to the combustion chamber in the form of hot streaks effecting combustion chamber cooling.
Today, a majority of land-based gas turbine engines operate on a gas fuel, such as natural gas, in order to limit harmful emissions to the atmosphere. Therefore, it is necessary to provide an ignition system that primarily operates on gas while having the capability of operating on a liquid fuel, as well while avoiding the issues identified in the prior art relating to start-up reliability, prolonged exposure to combustion temperatures, fuel blockage/coking in the ignition system, and hot streaks in the combustion chamber associated with continuous operation.